One of well-known conventional arts for a data communication system is a technique to set physical protocol such as a baud rate and clock polarity phase in correspondence to a physical data communication means. (For example, see Japanese Patent Laid-Open No. 2000-257501 (Page 25, FIG. 3, 300)) Another art is a technique using serial peripheral interface (hereinafter abbreviated as SPI) which is a clock synchronization serial bus communication having Chip Select signal lines as physical data communication means. (For example, see “MPC555 User's Manual MPC555UMJ/AD R0.95” (Pages 449 to 525)).